In some flat panel displays, a backplate is commonly separated from a faceplate using a spacer structure. In high voltage applications, for example, the backplate and the faceplate are separated by spacer structures having a height of approximately 1-2 millimeters. For purposes of the present application, high voltage refers to an anode to cathode potential greater than 1 kilovolt. In one embodiment, the spacer structure is comprised of several strips or individual wall structures each having a width of about 50 microns. The strips are arranged in parallel horizontal rows with each strip extending across the width of the flat panel display. The spacing of the rows of strips depends upon the strength of the backplate and the faceplate and the strips. Because of this, it is desirable that the strips be extremely strong. The spacer structure must meet a number of intense physical requirements. A detailed description of spacer structures is found in commonly-owned co-pending U.S. patent application Ser. No. 08/683,789 by Spindt et al. entitled "Spacer Structure for Flat Panel Display and Method for Operating Same". The Spindt et al. application was filed Jul. 18, 1996, and is incorporated herein by reference as background material.
In a typical flat panel display, the spacer structure must comply with a long list of characteristics and properties. More specifically, the spacer structure must be strong enough to withstand the atmospheric forces which compress the backplate and faceplate towards each other. Additionally, each of the rows of strips in the spacer structure must be equal in height, so that the rows of strips accurately fit between respective rows of pixels. Furthermore, each of the rows of strips in the spacer structure must be very flat to insure that the spacer structure provides uniform support across the interior surfaces of the backplate and the faceplate.
The spacer structure must also have good stability. More specifically, the spacer structure should not degrade severely when subjected to electron bombardment. As yet another requirement, a spacer structure should not significantly contribute to contamination of the vacuum environment of the flat panel display or be susceptible to contamination that may evolve within the tube.
In some conventional prior art spacer structures, a spacer wall is completely covered with a coating. However, in such prior art spacer structures, the coating material is not tailored for the variation in energy of the electrons which may potentially strike the spacer structure. That is, electrons impinging on the spacer structure near the cathode have an energy which is typically much less than the energy of electrons which strike the spacer structure near the anode. As a result of the variation in energy of impinging electrons, the secondary emission coefficient function of the wall will also vary significantly from the portion of the spacer structure near the cathode to the portion of the spacer structure near the anode.
Thus, need exists for a spacer structure which is at least partially coated with a material tailored for the variation in energy of the electrons which may potentially strike the spacer structure. A further need exists for a spacer structure which meets the above need and which does not degrade severely when subjected to electron bombardment. Still another need exists for a spacer structure which does not significantly contribute to contamination of the vacuum environment of the flat panel display or be susceptible to contamination that may evolve within the tube.